Composition of encapsulated chemical additives and methods for preparation of the same

ABSTRACT

Embodiments provide a method of encapsulating a solid cement additive. The method includes the step of applying a base film-forming monomer to the solid cement additive. The method includes the step of forming a coating layer surrounding the solid cement additive. The coating layer includes the base film-forming monomer. The method includes the step of applying an overlay film-forming monomer to the coating layer surrounding the solid cement additive. The method includes the step of reacting the base film-forming monomer and the overlay film-forming monomer to produce a polymer shell. The solid cement additive includes solid particles useful in cementing applications. The polymer shell includes a crosslinked polymer. The polymer shell surrounds the solid cement additive. The polymer shell has a permeability to water allowing controlled release of the solid cement additive.

RELATED APPLICATION

This application is related to, and claims priority from, U.S.Provisional Patent Application No. 62/612,756, filed on Jan. 2, 2018,the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND 1. Technical Field

Embodiments of the disclosure relate to chemical additives useful incementing applications. In particular, embodiments of the disclosurerelate to encapsulated chemical additives for controlled releaseapplications in cement slurries under downhole conditions.

2. Related Art

In many wellbores, cement can be used to form an annular barrier layerbetween a casing and the formation, or between two casings. Design ofcement slurries employed to seal the annuli requires addition of severaladditives. The additives are incorporated to address requirements forsafe and effective placement of a cement slurry in downhole conditions,and setting of the cement slurry into a competent sealant for theduration of the well life. Some additives, such as set accelerators andset retarders, are designed to control set times at downholetemperatures. Some additives, such as cement dispersants andviscosifiers, are designed to control slurry rheologies, such that thecement slurries can be pumped and placed in the zone of interest withoutthe use of excessive injection pressures. Additives, such as fluid losscontrol agents, can be used to prevent loss of the mixing fluid into theformation, causing dehydrated cement columns and bridges. Additives,such as gas migration control additives, can also be added to cementslurries when they are placed against formations that contain gasesunder pressure. The gas migration control additives function either byshortening the duration during which the cement paste is vulnerable togas penetration, such gas penetration capable of forming permanent flowchannels in the set cement, or prevent the slurry from prematuregelation prior to hydration.

One problem encountered in cement slurry design is excessive slurryviscosities at the mixing time due to the addition of viscosifiers tocompensate for any thermal thinning while pumping the slurry downhole.Another problem in designing cement slurries is due to detrimentalcompetitive adsorption on cement surfaces between fluid loss additives,some classes of dispersants and retarders and render them less effectivethan they would be in the absence of such fluid loss additives. Anoperationally impractical way to handle such problems would be to addsequentially different additives to slurries, for example, by injectingthe additives into the slurries at different times. Thus, there is aneed to develop additives modified such that they are released intoslurries in a sequential manner even when added together with all theother additives.

SUMMARY

Embodiments of the disclosure relate to chemical additives useful incementing applications. In particular, embodiments of the disclosurerelate to encapsulated chemical additives for controlled releaseapplications in cement slurries under downhole conditions.

In a first aspect, a method of encapsulating a solid cement additive isprovided. The method includes the step of applying a base film-formingmonomer to the solid cement additive. The method includes the step offorming a coating layer surrounding the solid cement additive. Thecoating layer includes the base film-forming monomer. The methodincludes the step of applying an overlay film-forming monomer to thecoating layer surrounding the solid cement additive. The method includesthe step of reacting the base film-forming monomer and the overlayfilm-forming monomer to produce a polymer shell. The solid cementadditive includes solid particles useful in cementing applications. Thepolymer shell includes a crosslinked polymer. The polymer shellsurrounds the solid cement additive. The polymer shell has apermeability to water allowing controlled release of the solid cementadditive.

In certain aspects, the base film-forming monomer includes a hydrophobicmonomer and the overlay film-forming monomer includes a hydrophilicmonomer. In certain aspects, the hydrophobic monomer includes carboxylicacid chlorides, carboxylic acid anhydrides, and combinations of thesame. In certain aspects, the hydrophilic monomer includespara-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimines, polyetheramines, andcombinations of the same.

In certain aspects, the base film-forming monomer includes a hydrophilicmonomer and the overlay film-forming monomer includes a hydrophobicmonomer. In certain aspects, the hydrophilic monomer includespara-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimines, polyetheramines, andcombinations of the same. In certain aspects, the hydrophobic monomerincludes carboxylic acid chlorides, carboxylic acid anhydrides, andcombinations of the same. In certain aspects, the hydrophobic monomer isan acyl chloride containing two or more acid chloride groups. In certainaspects, the carboxylic acid chlorides includes tricarboxyl acidchlorides, dicarboxylic acid chlorides, and combinations of the same. Incertain aspects, the tricarboxyl acid chloride includes1,3,5-benzenetricarbonyl trichloride. In certain aspects, thedicarboxylic acid chloride includes sebacoyl chloride, adipoyl chloride,and combinations of the same. In certain aspects, the carboxylic acidanhydride includes hexanedioic di(2,4,6-trimethylbenzoic acid,1,4-phthalic di(2,4,6-trimthylbenzoic) anhydride.

In certain aspects, the solid cement additive includes set accelerators,anti-gas migration additives, viscosifying agents, fluid loss controlagents, cement dispersants, retarders, salts, polymers, and combinationsof the same. In certain aspects, the size of the solid particles is lessthan about 500 micrometers. In certain aspects, the amount of the basefilm-forming monomer in the coating layer is in the range from about 1weight percent (wt. %) to about 25 wt. % of the solid cement additive.

In certain aspects, the crosslinked polymer includes polyamides,aramides, and combinations of the same.

In a second aspect, a method of using an encapsulated additive in acementing application is provided. The method includes the step ofmixing the encapsulated additive with a cement slurry to produce anadditive slurry. The cement slurry includes a cement and a mix water.The encapsulated additive is formed by the step of applying a basefilm-forming monomer to a solid cement additive. The encapsulatedadditive is formed by the step of forming a coating layer surroundingthe solid cement additive. The coating layer includes the basefilm-forming monomer. The encapsulated additive is formed by the step ofapplying an overlay film-forming monomer to the coating layersurrounding the solid cement additive. The encapsulated additive isformed by the step of reacting the base film-forming monomer and theoverlay film-forming monomer to produce a polymer shell. The polymershell includes a crosslinked polymer. The polymer shell surround thesolid cement additive. The polymer shell has a permeability to waterallowing controlled release of the solid cement additive. The methodincludes the step of placing the additive slurry in a formation. Themethod includes the step of releasing the solid cement additive from thesurrounding polymer shell.

In certain aspects, the cement includes a Portland cement, an aluminatecement, a Sorel cement, a phosphate cement, a pozzalonic cement, a slagcement, a geopolymer cement, and combinations of the same. In certainaspects, the mix water includes fresh water, sea water, a brine, andbrackish water.

In certain aspects, the crosslinked polymer includes polyamides,aramides, and combinations of the same.

In certain aspects, the solid cement additive includes set accelerators,anti-gas migration additives, viscosifying agents, fluid loss controlagents, cement dispersants, retarders, salts, polymers, and combinationsof the same.

In certain aspects, the base film-forming monomer includes a hydrophobicmonomer and the overlay film-forming monomer includes a hydrophilicmonomer. In certain aspects, the hydrophobic monomer includes carboxylicacid chlorides, carboxylic acid anhydrides, and combinations of thesame. In certain aspects, the hydrophilic monomer includespara-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimines, polyetheramines, andcombinations of the same.

In certain aspects, the base film-forming monomer comprises ahydrophilic monomer and the overlay film-forming monomer comprises ahydrophobic monomer. In certain aspects, the hydrophilic monomerincludes para-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimines, polyetheramines, andcombinations of the same. In certain aspects, the hydrophobic monomerincludes carboxylic acid chlorides, carboxylic acid anhydrides, andcombinations of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope of thepresent disclosure will become better understood with regard to thefollowing descriptions, claims, and accompanying drawings. It is to benoted, however, that the drawings illustrate only several embodiments ofthe disclosure and are therefore not to be considered limiting of thedisclosure's scope as it can admit to other equally effectiveembodiments.

FIGS. 1A-C are photographical representations of the encapsulatedadditive samples from the example showing gradual release of theadditive into water.

FIG. 2 is a graph of the release rates of the encapsulated additive as afunction of time and the weight percent of polymer shell.

FIG. 3 is a graph of the decrease in solid cement additive concentrationas the concentration of monomer increases.

In the accompanying Figures, similar components or features, or both,may have a similar reference label.

DETAILED DESCRIPTION

So that the manner in which the features and advantages of theembodiments of composition and methods, as well as others, which willbecome apparent, may be understood in more detail, a more particulardescription of the embodiments of the present disclosure brieflysummarized previously may be had by reference to the embodimentsthereof, which are illustrated in the appended drawings, which form apart of this specification. While the scope of the composition andmethod will be described with several embodiments, it is understood thatone of ordinary skill in the relevant art will appreciate that manyexamples, variations and alterations to the apparatus and methodsdescribed here are within the scope and spirit of the embodiments.Accordingly, the embodiments described are set forth without any loss ofgenerality, and without imposing limitations, on the embodiments. Thoseof skill in the art understand that the scope includes all possiblecombinations and uses of particular features described in thespecification.

Described here are compositions for cement additives. The cementadditives can be encapsulated for use in cementing applications. Theencapsulated additives can be used in downhole cementing applications.

As used here, “melting temperature” or “melting point” refers to thetemperature at which a monomer or polymer transitions from a crystallineor semi-crystalline state to a liquid phase.

As used here, “softening temperature” refers to the minimum temperature,such that all temperatures greater than the softening temperature, thatcauses amorphous solids, with no definite melting point, becomes softerand rubbery (in the case of plastics), and ultimately become flowableliquids at sufficiently high temperatures.

As used here, “deform” means distort the shape or form of; makemisshapen.

As used here, “degrade” means break down, break apart or deteriorate.Degrade can include forming new molecules or molecular fragments.

As used here, “aramide” refers to an aromatic polyamide. Terms such as“aramids,” “aramides,” “polyaramids,” “polyaramides,” “aramid polymers,”“aramide polymers,” and “aromatic polyamides” are used interchangeably.Commercial examples of aramides include para-aramides such as Kevlar®(available from DuPont®, Wilmington, Del.), Technora® (available fromTeijin Aramid USA, Inc, Conyers, Ga.), Twaron® (available from TeijinAramid USA, Inc, Conyers, Ga.), and Heracron® (available from KolonIndustries, Inc., Gwachon, Korea), and meta-aramides such as Nomex®(available from DuPont®, Wilmington, Del.) and Teijinconex® (availablefrom Teijin Aramid USA, Inc, Conyers, Ga.). A para-aramide is an aramidewhere the polymer chain is connected via the para positions of an acylgroup subunit or functional group. A meta-aramide is an aramide wherethe polymer chain is connected via the meta positions of an acyl groupsubunit or functional group.

The encapsulated additives include a solid cement additive and a polymershell.

The solid cement additive is any solid, particulate that does notplastically deform or flow upon application of force, such that theparticulates are free flowing and useful in downhole applications. Thesolid cement additive can include dry, gelled or gelatinous materials,so long as they are free flowing. The solid cement additive can haveinternal voids with a matrix-like structure. The solid cement additivecan include solid particles. The solid cement additive can be any cementadditive useful in cementing applications. The solid cement additive canbe water-soluble. The solid cement additive can be selected from setaccelerators, anti-gas migration additives, viscosifying agents, fluidloss control agents, cement dispersants, retarders, salts, polymers, andcombinations of the same. Examples of set accelerators include calciumchlorides, calcium nitrite, and combinations of the same. In at leastone embodiment, the solid cement additives can be water soluble. Thesolid cement additives can have a particle size, measured by thediameter. The median particle size (particle size D₅₀) can be about 600micrometers (μm) or less and alternately about 500 μm or less. Themedian particle size can be measured by particle size measuringinstruments. In at least one embodiment, the solid cement additive issolvent-free, that is, the solid cement additive is not solubilized inwater for encapsulation purposes.

The polymer shell completely surrounds and encapsulates the solid cementadditive. The polymer shell includes a crosslinked polymer. Examples ofthe crosslinked polymer include polyamides, aramides, and combinationsof the same. In at least one embodiment, the crosslinked polymer is apolyamide that does not contain aromatic monomers. The polymer shell canhave a permeability to water. The permeability of the polymer shell canfunction as a permeable membrane or a semi-permeable membrane. Asemi-permeable membrane allows solvents, such as water to pass through,whereas a permeable membrane allows solvents such as water and solutessuch as ions and molecules to pass through. In at least one embodiment,the polymer shell is permeable to water. The polymer shell can be heatresistant, such that the polymer shell does not deform or degrade atdownhole temperatures. Downhole temperatures can be in the range betweenabout 60 deg F. and about 550 deg F. The polymer shell can have aspecific gravity between about 1.2 and about 1.4. The polymer shell canhave a glass transition temperature of greater than about 150 deg C.,alternately a glass transition temperature of about 200 deg C. Thepolymer shell does not dissolve in aqueous solutions. In someembodiments, the polymer shell does not dissolve in non-aqueous fluids.In at least one embodiment, the polymer shell is formed in the absenceof a catalyst. In at least one embodiment, the polymer shell is formedat room temperature.

The encapsulated additives can be prepared by a dry coating method.Examples of dry coating methods include fluid dry coating and drycoating by hot rolling. The dry coating methods do not include a step ofcreating an emulsion. In a dry coating method two film-forming monomersare applied in sequence directly to the solid cement additive and thecrosslinked polymer forms upon contact between the two film-formingmonomers. The crosslinked polymer encapsulates the solid cementadditive.

In the fluid dry coating method, the film-forming monomers can be bothin fluid form or a combination where one is in molten form and the otheris in solid form at the time of mixing.

Forming the Coating Layer

The base film-forming monomer is applied to the solid cement additive toform a coating layer surrounding the solid cement additive. The coatinglayer coats and surrounds each solid particle of the solid cementadditive. The amount of the base film-forming monomer in the coatinglayer can be between about 1 wt. % and about 25 wt. % of the solidcement additive.

The base film-forming monomer can be applied as a base monomer fluidusing a fluid dry coating method and alternately as a solid base monomerusing a dry coating by hot rolling method.

In the fluid dry coating method, the base monomer fluid can first beproduced. Examples of the base monomer fluid can include a base moltenmonomer and a base monomer solution. The base molten monomer can beobtained by heating the base film-forming monomer to a temperature at orgreater than the melting temperature of the base film-forming monomer.The base monomer solution can be obtained by dissolving the basefilm-forming monomer in a non-aqueous solvent. The non-aqueous solventcan be an anhydrous or nearly anhydrous solvent containing less thanabout 5 wt. % water. Examples of the non-aqueous solvent can includealcohols, alcohol ethers, ethers, aromatic hydrocarbons, and halogenatedsolvents. The base film-forming monomer can be soluble in thenon-aqueous solvent at room temperature with solubility of greater thanabout 50 wt. % and alternately greater than about 70 wt. %. Then, thebase monomer fluid can be applied to the solid cement additive to formthe coating layer surrounding the solid cement additive. Methods ofapplying the base monomer fluid can include pan coating and drumcoating. In pan coating methods, the solid cement additives are tumbledin a rotating pan, alternately are tumbled in a drum equipped with vaporremoval equipment, and alternately are placed in other devices while thebase monomer fluid is applied in a controlled addition. Examples ofcontrolled addition include spray coating and drip addition. In drumcoating methods, the solid cement additive and base monomer fluid aremixed in a rolling drum, alternately on a moving belt, and alternatelyin a fluidized reactor. Vapor removal equipment can be used. When thebase monomer fluid includes a base monomer solution, the non-aqueoussolvent can be evaporated during the step of applying the base monomerfluid to the solid cement additive. It is understood, the coating layersurrounding the solid cement additives can begin to form during the stepof applying the base monomer fluid to the solid cement additives and canthen continue after the base monomer fluid has been applied to the solidcement additives. In at least one embodiment, the temperature of thesolid cement additive with the coating layer is reduced to below themelting temperature at the end of the step of forming the coating layer.

In the dry coating by hot rolling method, the solid base monomer caninclude the base film-forming monomer in the form of pellets, flakes,granules, powders, and combinations of the same. The solid base monomeris blended with the solid cement additive to form an additive monomerblend. The additive monomer blend is hot rolled at a temperature at orgreater than the melting temperature and alternately a temperature at orgreater than the softening temperature of the base film-forming monomer.The additive monomer blend is hot rolled such that the base film-formingmonomer forms a coated layer around the solid cement additive. Thecondensation reaction for forming the polymer shell of the vesicle isnot initiated by the hot rolling process; however the elevatedtemperature can subsequently facilitate the condensation reactionbetween the base film-forming monomer and the overlay film-formingmonomer. The time for dry coating by hot rolling can depend on the basefilm-forming monomer used, the temperature at which hot rolling occurs.In at least one embodiment, hot rolling can continue in the range fromabout 2 hours to about 24 hours. In at least one embodiment, hot rollingcan continue in the range from about 2 hours to about 8 hours. Hotrolling continues until the base film-forming monomer forms the coatinglayer surrounding the solid cement additive. The extent and depth of thecoating layer can be periodically measured by any known measurementmethod. In at least one embodiment, the depth of the coating layer canbe measured by thermogravimetric analysis. In at least one embodiment,hot rolling continues until the coating layer uniformly surrounds thesolid cement additive. As used throughout, “uniformly” means evenly withvariation of less than about 5%. In at least one embodiment, thetemperature of the solid cement additive with the coating layer isreduced to below the melting temperature at the end of the step offorming the coating layer. Hot rolling continues during the entirety ofthe step of forming the coating layer.

Adding the Overlay Monomer

The overlay monomer can be applied to the coating layer surrounding thesolid cement additive. The amount of the overlay film-forming monomerapplied to the coating layer can be in the range between about 1 wt. %and about 40 wt. % of the solid cement additive. The overlayfilm-forming monomer can be applied as an overlay monomer fluid using afluid dry coating method and alternately as a solid overlay monomerusing a dry coating by hot rolling method.

In the fluid dry coating method, the overlay monomer fluid can first beformed. Examples of the overlay monomer fluid include an overlay moltenmonomer and an overlay monomer solution. The overly molten monomer canbe obtained by heating the overlay film-forming monomer to a temperatureat or greater than the melting temperature of the overlay film-formingmonomer. The overlay monomer solution can be obtained by dissolving theoverlay film-forming monomer in a non-aqueous solvent. The non-aqueoussolvent can be an anhydrous or nearly anhydrous solvent containing lessthan about 5 wt. % water. Examples of the non-aqueous solvent caninclude alcohols, alcohol ethers, ethers, aromatic hydrocarbons, andhalogenated solvents. The base film-forming monomer can be soluble inthe non-aqueous solvent at room temperature with a solubility of greaterthan about 50 wt. % and alternately greater than about 70 wt. %. Theoverlay monomer fluid can be applied to the coating layer surroundingthe solid cement additive. Methods of applying the overlay monomer fluidcan include pan coating and drum coating. In pan coating methods, thesolid cement additive with the coating layer are tumbled in a rotatingpan, alternately are tumbled in a drum equipped with vapor removalequipment, and alternately in other devices, while the overlay monomerfluid is applied in a controlled addition. Examples of controlledaddition include spray coating and drip addition. In drum coatingmethods, the solid cement additive with coating layer and the overlaymonomer fluid are mixed in a rolling drum, alternately placed on amoving belt, and alternately in a fluidized reactor. Vapor removalequipment can be used. When the overlay monomer fluid includes anoverlay monomer solution, the non-aqueous solvent can be evaporatedduring the step of applying the base monomer fluid to the solid cementadditive.

In the dry coating by hot rolling method, the solid overlay monomer caninclude the overlay film-forming monomer in the form of pellets, flakes,granules, powders, and combinations of the same. The solid overlaymonomer can be mixed with the solid cement additive with the coatinglayer. The mixture is hot rolled at a temperature at or greater than themelting temperature of the overlay film-forming monomer. The extent anddepth of the coating layer can be periodically measured by any knownmeasurement method. In at least one embodiment, the depth of the coatinglayer can be measured by thermogravimetric analysis. In at least oneembodiment, hot rolling continues until the coating layer uniformlysurrounds the solid cement additive. The time for dry coating by hotrolling can depend on the overlay film-forming monomer used, thetemperature at which hot rolling occurs. In at least one embodiment, hotrolling can continue in the range from about 2 hours to about 24 hours.In at least one embodiment, hot rolling can continue in the range fromabout 2 hours to about 8 hours. In at least one embodiment, the mixtureis hot rolled at a temperature at or greater than the meltingtemperature of base film-forming monomer.

Forming the Encapsulated Additive

The overlay film-forming monomer reacts with the base film-formingmonomer to produce the polymer shell, where the polymer shell containsthe crosslinked polymer. In at least one embodiment, the polymer shellis formed while the solid particles are agitated. The crosslinkedpolymer surrounds the solid cement additive forming the polymer shell.The solid cement additives with coating layer can be subjected to vaporremoval while the reaction to produce the crosslinked polymer occurs.The vapor removal methods can include placing the process under vacuumand alternately by flowing a stream of an inert gas, alternately air,over the solid cement additives.

The reaction between the base film-forming monomer and the overlayfilm-forming monomer can be a polymer condensation reaction. In at leastone embodiment, the reaction is carried out at room temperature. Thebase film-forming monomer and the overlay film-forming monomer react atthe point of contact between the two layers to form a polymer. Thepolymer condensation reaction can produce a byproduct. As an example,when the base film-forming monomer is a carboxylic acid chloride and theoverlay film-forming monomer is a polyamine, the byproduct is hydrogenchloride. As used here, “polyamine” refers to an organic compound havingmore than one amino groups. The number of primary amine groups per apolyamine molecule is at least two. The hydrogen chloride can be removedby the vapor removal methods. By way of example, when the basefilm-forming monomer is a carboxylic acid anhydride and the overlayfilm-forming monomer is a polyamine, the byproduct is water which can beremoved by the vapor removal methods. In at least one embodiment, theproduced polymer is chemically inert and thermally resistant.

In at least one embodiment, the reaction between the base film-formingmonomer and the overlay film-forming monomer begins to occur as theoverlay monomer fluid is applied to the coating layer surrounding thesolid cement additive and continues after all of the overlay monomerfluid is added. In at least one embodiment, the reaction between thebase film-forming monomer and the overlay film-forming monomer begins tooccur at some point after the overlay monomer fluid is applied to thecoating layer surrounding the solid cement additive and continues afterall of the overlay monomer fluid is added. In at least one embodiment,the reaction between the base film-forming monomer and the overlayfilm-forming monomer does not begin until after all of the overlaymonomer fluid is applied to the coating layer surrounding the solidcement additive. In at least one embodiment, the reaction between thebase film-forming monomer and the overlay film-forming monomer does notbegin until the solid cement additive coated with the base film-formingmonomer and the overlay film-forming monomer is heated to a temperaturegreater than the reaction temperature for either the base-film formingmonomer or the overlay film-forming monomer.

The total amount of the base film-forming monomer and the overlayfilm-forming monomer can be in the range between about 5 wt. % and about100 wt. % of the solid cement additive, alternately between about 2 wt.% and about 65 wt. % of the solid cement additive.

The step of applying the overlay monomer fluid to the coating layersurrounding the solid cement additives must occur after the step offorming the coating layer.

The solid cement additives surrounded by the polymer shell form theencapsulated additives. The size of the encapsulated additives can bemeasured by methods for measuring particle size distribution.

In at least one embodiment, the encapsulated additives do not containagglomerations of the solid particles of the solid cement additivesurrounded by a polymer shell. In at least one embodiment, theencapsulated additives can be sieved through sieves to remove anyagglomerated particles of the encapsulated additives of sizes greaterthan about 1,000 μm, such as a mesh of size No. 18 (1.00 millimeter(mm)) with a 1.00 mm (1,000 μm) sieve opening. In at least oneembodiment, the methods of forming the encapsulated are in the absenceof a step to form an emulsion.

The base film-forming monomer can include a hydrophilic monomer and ahydrophobic monomer. The overlay film-forming monomer can include ahydrophilic monomer and a hydrophobic monomer. When the basefilm-forming monomer is a hydrophilic monomer, the overlay film-formingmonomer is a hydrophobic monomer. When the base film-forming monomer isa hydrophobic monomer, the overlay film-forming monomer is a hydrophilicmonomer.

The hydrophilic monomer can be a hydrophilic monomer having at least tworeactive groups capable of reacting with those on the hydrophobicmonomer. By way of example, when the hydrophilic monomer is a polyamine,the number of primary amine groups per molecule is at least two. In atleast one embodiment, the hydrophilic monomer is a polyamine containingat least two or more primary amine groups. Examples of polyaminessuitable for use as the hydrophilic monomers can includepara-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimine, polyetheramines, andcombinations of the same.

The hydrophobic monomer can be a hydrophobic monomer having at least tworeactive groups capable of reacting with those on the hydrophilicmonomer. In at least one embodiment, the hydrophobic monomer is an acylchloride containing two or more acid chloride groups. By way of example,if the hydrophobic monomer is a carboxylic acid chloride, the number ofacid chloride groups per molecule is at least two. Examples ofhydrophobic monomers can include carboxylic acid chlorides, carboxylicacid anhydrides, and combinations of the same. Examples of carboxylicacid chlorides include tricarboxyl acid chlorides, dicarboxylic acidchlorides, and combinations of the same. Examples of tricarboxyl acidchlorides include 1,3,5-benzenetricarbonyl trichloride. Examples ofdicarboxylic acid chlorides can include sebacoyl chloride, adipoylchloride, and combinations of the same. Examples of carboxylic acidanhydrides can include hexanedioic di(2,4,6-trimethylbenzoic) acid,1,4-phthalic di(2,4,6-trimethylbenzoic) anhydride, and combinations ofthe same.

The permeability of the polymer shell can control the rate of release ofthe solid cement additive. The amount of the base film-forming monomerand overlay film-forming monomer can be adjusted to control thereactivity rate between the base film-forming monomer and overlayfilm-forming monomer, the permeability, and the thickness of theresulting polymer shell. The molar ratio of the hydrophobic monomer tothe hydrophilic monomer can be in the range between about 1:1 and about2:1. Alternately, the molar ratio of reactive groups on the hydrophobicmonomer to the reactive groups on the hydrophilic monomers is in therange between about 0.3 to about 1 and about 1 to about 0.3.

The encapsulated additives can be mixed with a cement slurry to producean additive slurry. The cement slurry can include a cement and a mixwater. The encapsulated additives are mixed with a cement slurry at anytime prior to the cement slurry being introduced to a formation. In atleast one embodiment, the encapsulated additives can be dry blended withthe cement to form a free-flowing dry powder before the mix water isadded to produce the cement slurry. In at least one embodiment, theencapsulated additives can be added to the mix water prior to theaddition of the cement. In at least one embodiment, the encapsulatedadditives can be injected into the cement slurry or the mix water aspart of a liquid emulsion.

The cement can be any type of cement useful in downhole cementingapplications. Examples of the cement include a Portland cement, analuminate cement, a Sorel cement, a phosphate cement, a pozzaloniccement, a slag cement, and a geopolymer cement. Examples of the mixwater include fresh water, sea water, a brine, and brackish water. In atleast one embodiment, two or more encapsulated additives can be added tothe cement slurry, such that two or more different cement additives arecarried into the cement slurry. In at least one embodiment, a blend ofencapsulated additives and solid cement additives can be added to thecement slurry. The encapsulated additives can be mixed within the cementslurry to distribute the encapsulated additives through the additiveslurry. Other additives can be added to the additive slurry. Examples ofother additives can include dispersants, retarders, accelerators,viscosifiers, fluid loss control agents, light weight additives, highdensity additives, free water reducing agents, gas phase, surfactants,gas migration additives, lattices, elastomers, fibers, and combinationsof the same.

The concentration of the encapsulated additives in the additive slurrywill vary depending on the solid cement additive encapsulated and theintended function of the solid cement additive. The concentration of theencapsulated additive can be in the range from about 0.1% by weight ofcement to about 25% by weight of cement.

The encapsulated additives can be added to the cement slurry in acontinuous process or in a batch mixer.

The additive slurry can be placed in the formation according to anyprocess for placing cementing in a wellbore or formation. In at leastone embodiment, the cement slurry can be pumped downhole and can beallowed to set. In at least one embodiment, the cement slurry can beplaced in an annulus between two casings and can be allowed to set. Inat least one embodiment, the cement slurry can be pumped between acasing and the formation and allowed to set.

The polymer shell can be designed such that the solid cement additive isreleased from the polymer shell into the cement slurry prior to thecement setting. The polymer shell can be designed such that the solidcement additive is released during the preparation of the cement slurry,prior to pumping the cement slurry downhole, during the pumping process,but prior to placement of the cement slurry downhole, or after thecement is placed downhole. The design of the release of the solid cementadditive can be based on the type of solid cement additive.

The solid cement additive can pass intact from the polymer shell.

After the solid cement additive is depleted within the polymer shell, ahollow polymer shell remains. Advantageously, the hollow polymer shellcan be incorporated in the hardened cement imparting additionalmechanical properties to the hardened cement. Advantageously, the hollowpolymer shell is heat resistant.

EXAMPLE

Methods of Making Encapsulated Additive

Encapsulated additive samples were prepared by two different dry coatingmethods. The solid cement additive was a cement dispersant. The cementdispersant was a sulfonated-acetone-formaldehyde condensate (SAFC), ared powder, used for its strong colorimetric signal. The hydrophilicmonomer used was 1,6-hexanediamine (HDA). The hydrophobic monomer usedwas 1,3,5-benzenetricarbonyl trichloride (BTCAC). Samples were preparedwith the amount of each monomer shown in Table 1.

TABLE 1 Amount of monomers in each sample Base Overlay Film- Wt. % ofFilm- Amount of Wt. % of Forming Amount of 1^(st) 1^(st) Forming 2^(nd)Monomer 2^(nd) Sample Method Monomer Monomer (g) Monomer Monomer (g)Monomer 1 1 HDA 0.1 5 BTCAC 0.2 10 2 1 HDA 0.2 10 BTCAC 0.3 15 3 1 HDA0.3 15 BTCAC 0.5 20 4 1 HDA 0.5 20 BTCAC 0.6 30 5 2 BTCAC 0.1 5 HDA 0.210 6 2 BTCAC 0.3 15 HDA 0.5 25 7 2 BTCAC 0.5 25 HDA 0.8 40

In a first method, Method 1, an amount of the hydrophilic monomer wasadded as the base film-forming monomer and an amount of the hydrophobicmonomer was added as the overlay film-forming monomer. In a secondmethod, Method 2, an amount of the hydrophobic monomer was added as thebase film-forming monomer and an amount of the hydrophilic monomer wasadded as the overlay film-forming monomer. In each method the followingsteps were employed:

1. The base film-forming monomer and overlay film-forming monomer werewarmed in separate water baths at 60 deg C. until melted to produce abase monomer fluid and an overlay monomer fluid.

2. Two grams of the cement additive was added to 20 milliliter (mL)vials.

3. A rolling oven was set at 120 deg F. (49 deg C.).

4. The base monomer fluid in the amount listed in Table 1 was addeddropwise to the vials containing the cement additive.

5. The sample vials were placed into the rolling oven for 4 hours, withthe rollers on, allowing coating of the samples with the basefilm-forming monomer forming the coating layer surrounding the solidcement additive.

6. The overlay monomer fluid in the amount listed in Table 1 was addeddropwise to the vials containing the solid cement additives with thecoating layer.

7. The sample vials were placed into the rolling oven for 4 hours, withthe rollers on, allowing coating of the samples with the overlayfilm-forming monomer.

8. Allowing a polymer condensation reaction to occur between the basefilm-forming monomer and the overlay film-forming monomer to form thepolymer shell.

The method resulted in encapsulated additives in the form of particles.

Methods of Using the Encapsulated Additive

The slow release of the encapsulated additives in an aqueous medium wasevaluated by two methods. The first method was by visual means ofobservation where the Sample 1 particle of the encapsulated additiveproduced by Method 1 was placed in a beaker of water and the diffusionof the colored streak into the water from the encapsulated additive wasobserved.

FIG. 1A shows the encapsulated additive 100 at t₁ (0 minutes).

FIG. 1B shows the encapsulated additive 110 at t₂ (15 minutes). As canbe seen by the darker stream, the solid cement additive is escaping thepolymer shell. At t₃ (30 minutes), the solid cement additive is releasedcompletely. As shown in FIG. 1C, the solid cement additive is depletedfrom the polymer shell 120, where only the empty polymer shell 120 canbe observed.

In a second method, quantitative measurements of the release rates forsamples 1-4 were obtained using an ultraviolet-visible (UV/Vis)spectrophotometer (λ_(max)=420 nm, from Hach, Loveland, Colo.). TheUV/Vis spectrophotometer was used to measure the absorbance of thereleased additive as a function of time and the weight percent of thefirst film-forming monomer. The results are shown in FIG. 2.

FIG. 2 is a graphical representation 200 showing UV/Vis absorbance ofthe released additive in Samples 1-4 in Table 1 as a function of time.The horizontal axis represents time in seconds. The vertical axisrepresents UV/Vis absorbance in arbitrary units. Square points 210represent absorbance of Sample 1 in Table 1 having 5% wt. % HDA.Circular points 220 represent absorbance of Sample 2 in Table 1 having10% wt. % HDA. Triangular points 230 represent absorbance of Sample 3 inTable 1 having 15% wt. % HDA. Cross-shaped points 240 representabsorbance of Sample 4 in Table 1 having 20% wt. % HDA.

The results show that as the weight percent of the first film-formingmonomer is increased the additive release rate is reduced. The decreasein additive release rate as a function of the increase in polymer shellweight percent is shown in FIG. 3. FIG. 3 is a graphical representation300 showing the additive absorbance, which is the integrated area of thecurves shown in FIG. 2. The horizontal axis represents the weight ratioof the first film-forming for Samples 1-4 in Table 1. The vertical axisrepresents integrated values of the absorbance curves for Samples 1-4shown in FIG. 2 in arbitrary units.

Although the embodiments have been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade hereupon without departing from the principle and scope.Accordingly, the scope of the embodiments should be determined by thefollowing claims and their appropriate legal equivalents.

There various elements described can be used in combination with allother elements described here unless otherwise indicated.

The singular forms “a,” “an,” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed here as from about one particular value to aboutanother particular value and are inclusive unless otherwise indicated.When such a range is expressed, it is to be understood that anotherembodiment is from the one particular value to the other particularvalue, along with all combinations within said range.

As used here and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

That claimed is:
 1. A method of encapsulating a solid cement additivefor use in cementing applications, the method comprising the steps of:applying a base film-forming monomer to the solid cement additive usingat least one of a fluid dry coating method and a dry coating by hotrolling method such that a coating layer is formed surrounding the solidcement additive, the coating layer comprising the base film-formingmonomer; applying an overlay film-forming monomer to the coating layersurrounding the solid cement additive using the at least one of thefluid dry coating method and the dry coating by hot rolling method; andreacting the base film-forming monomer and the overlay film-formingmonomer to produce a polymer shell, where the solid cement additivecomprises solid particles, where the polymer shell comprises acrosslinked polymer, the crosslinked polymer comprising aramides, wherethe polymer shell surrounds the solid cement additive, and where thepolymer shell has a permeability to water allowing controlled release ofthe solid cement additive.
 2. The method of claim 1, where the basefilm-forming monomer comprises a hydrophobic monomer and the overlayfilm-forming monomer comprises a hydrophilic monomer.
 3. The method ofclaim 2, where the hydrophobic monomer is selected from the groupconsisting of carboxylic acid chlorides, carboxylic acid anhydrides, andcombinations of the same.
 4. The method of claim 2, where thehydrophilic monomer is selected from the group consisting ofpara-phenylenediamine, meta-phenylenediamine, ethylenediamine,hexamethylenediamine, polyethyleneimines, polyetheramines, andcombinations of the same.
 5. The method of claim 1, where the basefilm-forming monomer comprises a hydrophilic monomer and the overlayfilm-forming monomer comprises a hydrophobic monomer.
 6. The method ofclaim 5, where the hydrophilic monomer is selected from the groupconsisting of para-phenylenediamine, meta-phenylenediamine,ethylenediamine, hexamethylenediamine, polyethyleneimines,polyetheramines, and combinations of the same.
 7. The method of claim 5,where the hydrophobic monomer is selected from the group consisting ofcarboxylic acid chlorides, carboxylic acid anhydrides, and combinationsof the same.
 8. The method of claim 1, where the solid cement additiveis selected from the group consisting of set accelerators, anti-gasmigration additives, viscosifying agents, fluid loss control agents,cement dispersants, retarders, salts, polymers, and combinations of thesame.
 9. The method of claim 1, where the size of the solid particles isless than about 500 micrometers.
 10. The method of claim 1, where theamount of the base film-forming monomer in the coating layer is in therange from about 1 wt. % to about 25 wt. % of the solid cement additive.11. The method of claim 1, where the crosslinked polymer furtherincludes polyamides.